“Lamination” is the act of applying multiple layers of film to each other or to another substrate such as paper. This laminated structure can be produced with adhesives or by using a thermoplastic film that will adhere to itself and/or the paper substrate under hot conditions and pressure. Laminated films or structures will typically give good barrier properties preventing odor, grease, oil, moisture vapor and/or water-based materials from leaking through the laminated structure. In some instances, a specific form such as a drink cup or ice cream container will be formed so as to provide a vessel which will hold quantities of liquids. In these instances, the thermoplastic film will provide heat-sealing capability. In other words, the thermoplastic film under heat and pressure will now adhere to itself when formed into a cup or container.
The polymer typically used for heat-seal applications is polyethylene (PE). This coating is based on petroleum (i.e., ethylene) which is polymerized into a high molecular weight polymer. This can be extruded or laminated onto paper or board that is used in food and other packaging. For example, PE is used for most inner layers of packing materials. PE provides very good barrier properties (i.e., resistance to water, grease, oil and moisture vapor) and since it is thermoplastic at a low enough temperature, it can be heat-sealed to itself, providing a way to make the package without an additional adhesive being used. To achieve these properties, PE has to be properly applied and sufficiently thick.
Paper laminated or extrusion coated with PE will not decompose or biodegrade in landfill because of the PE. While it can be repulped and recycled, the fiber yield is low because the PE is bound so tightly to the paper substrate. When repulped, the PE with a fiber layer on it has to be taken from the repulper and sent to landfill. Most major retailers would like to stop using PE, but there is currently no suitable alternative.
A suitable heat-seal coating should be repulpable (when going through the recycled paper making process, will readily breakdown without any major amount of by-product that needs to be landfilled), recyclable (can be made into paper again), compostable (break down in a commercial composting facility) and biodegradable (decomposes into basic materials such as carbon dioxide, carbon monoxide and water).
Repulpability refers to the ability of paper packaging to be broken down when it is recycled at a paper mill. One common standard is that 80% of the fiber in the packaging has to be available for the recycled board during the repulping process for paper packaging to be considered repulpable.
Recyclability refers to the fiber from the repulping process being incorporated into paper sheet. For example, when 20% of the recovered fiber is combined with 80% virgin fiber, the resulting paper must have the same physical properties as a similar sheet made from 100% virgin fiber.
Biodegradability and compostability refer to products which are compostable in municipal and industrial composting facilities. Furthermore, the degradation of the specific materials must not diminish the value or utility of the compost resulting from the composting process.